genotypic variability S. aureus, P. aeruginosa and Bcc during chronic lung infection. Methods: The strains were studied by diagnostic algorithm: phenotypic and molecular techniques - antimicrobial susceptibility testing, PCR genotyping, MLST, NGS was carried. Results: The monitoring during 1–5 years showed that the effectiveness of antibiotic therapy of S. aureus infection was 46.6%, P. aeruginosa – 41%, Bcc – 0%. Sometimes after the elimination of S. aureus or P. aeruginosa in 1–6 month period strains of the same species that differed by phenotype and genotype were isolated. For example, the fact that the initial P. aeruginosa strain ST633 was changed by P. aeruginosa ST803 through 2 years and 6 month was proved by WGS. Another case was connected with the changes in the genome of the same genotype. The WGS of P. aeruginosa ST1050 strains isolated in 6 year period showed that the later strain acquired two genes of antibiotic resistance: aac(3)-IIa, (gentamicin resistance) and gene from bla TEM family. These genes were localized on plasmids. In case of pair of B. cenocepacia ST709 strains, more recent strain acquired the gene sul1 that induces sulfanilamide resistance. Conclusion: Our study allowed us to observe three variants of variability of pathogens in CF patients: 1. phenotypic variability (mucoid and non-mucoid colonies, scv-pheno- type, antibiotic resistance); 2. change of the S. aureus, P. aeruginosa genotype and the persistence of one Bcc genotype; 3. microevolution change in the genotype due to horizontal gene. The presence of different mechanisms of variability requires the perman- ent monitoring and the using of appropriate antibiotic treatment according to the type of variability. 163 Is diagnostic of Pseudomonas aeruginosa deficient in Bulgarian CF patients? G. Petrova 1 , P. Perenovska 1 , S. Lesichkova 2 , D. Miteva 1 , S. Lazova 1 , V. Issaev 1 , T. Strateva 3 . 1 University Hospital Alexandrovska, Pediatric Clinic, Medical University of Sofia, Sofia, Bulgaria; 2 University Hospital Alexandrovska, Clinical Immunology and Stem-cell Bank Department, Medical University of Sofia, Sofia, Bulgaria; 3 Department of Medical Microbiology, Faculty of Medicine, Medical University of Sofia, Sofia, Bulgaria Background: Patients with cystic fibrosis (CF) in nearly 30–35% have difficulties in expectorating sputum (even after induction), which may be the reason for the late detection of colonization with Pseudomonas aeruginosa and thus delayed implementing the eradication regimens. In the global standards for the treatment of patients with cystic fibrosis determination of antibodies to Pseudomonas aeruginosa is a major element in tracing these patients displacing even standard microbiological testing. Aim: To search for P. aeruginosa antibodies in patients with CF, even in the absence of a microorganism in the samples from respiratory tract (sputum, throat aspirate). Material and methods: From 140 CF patients (76 males, 64 females; aged from 0,1 to 65 years) we examined secretions from the airways for a precise microbiology identification. We used ELISA – ready kit for IgG antibodies to P. aeruginosa detection in peripheral venous blood. Results: Chronic infection with P. aeruginosa from respiratory samples is found in 91 patients (65,40%). From the rest 49 patients we could made ELISA test to 30, and we found 6 (20%) had elevated IgG levels towards P. aeruginosa, despite negative microbiology results. Conclusion: The percentage of chronic infection with P. aeruginosa is one of the highest reported in EU countries. Perhaps the differences are due to the fact that the test for antibodies is not routinely done in our practice and we rely mostly on sputum/throat swabs and sometimes we can’t have really early detection of colonization with P. aeruginosa and our eradication regimens are delayed. Acknowledgement: This work was supported by a grant from the Medical Universityof Sofia (Council of Medical Science, project no. 512/2016, grant no. 64/2016) 164 Are viral respiratory infections a real issue in infants with cystic fibrosis: preliminary results of a prospective cohort study M. Eymery 1 , P. Reix 1 , F. Morfin 2 , A. Doleans-Jordheim 3 , S. Vrielynck 1 , V. Jubin 1 , M. Perceval 1 . 1 Lyon 1 University, UMR5557, Pediatric Cystic Fibrosis Center, Bron, France; 2 Institut des Agents Infectieux and Lyon 1 University CIRI INSERM U1111, Hospices Civils de Lyon, Laboratoire de Virologie, Lyon, France; 3 Institut des Agents Infectieux and Lyon 1 University UMR5557-UCBL/CNRS/ VetAgroSup, Hospices Civils de Lyon, Laboratoire de Bactériologie, Lyon, France Objectives: In cystic fibrosis (CF) children, early viral respiratory tract infections (vRTI) may worsen lung disease and accelerate lung function decline. Our main objective was to determine the frequency of vRTI and the panel of viruses detected during a complete viral epidemic year. We also wanted to assess the short-term impact of the vRTI on hospitalizations, nutritional status and immediate bacteriological changes. Methods: Twenty-five CF children aged less than 24 months old were included and prospectively followed up. Nasal swabs were performed on a systematic basis. An additional swab was taken when vRTI was suspected. RT-PCR or PCR were performed to detect a panel of 8 viruses. Clinical, healthcare and microbiological outcomes were studied. Results: Fifteen infants have completed their one-year close follow-up so far. A mean of 3.5 vRTI per patient per year was found out. Avirus was detected in 65% of symptomatic patients and in 41% of asymptomatic ones. Picornaviruses were the most frequent for both groups. Three infants were hospitalized. One day of parental absenteeism was reported, and 1.2 additional medical consultations per patient were needed. Pseudomonas aeruginosa primocolonisation occurred for 12% of children and staphylo- coccical primocolonisation was documented for 56% of them. Antibiotics were used in 82.5% of vRTI. Conclusion: Preliminary results indicate that vRTI were usually non severe and of viral origin in two-third of cases. The impact on healthcare consumption seems low. The one-year follow-up will be completed for all patients within March 2017. Mid-term follow-up will evaluate the potential negative effects of early vRTI on functional and microbiological outcome measures with pulmonary function tests at the age of 6 and regular sputum bacteriological analyses. 165 Modeling polymicrobial infections in the pathogenesis of cystic fibrosis lung disease C. Cigana 1 , I. Bianconi 1 , M. De Simone 1 , C. Riva 2 , R. Baldan 2 , B. Sipione 1 , D.M. Cirillo 2 , A. Bragonzi 1 . 1 IRCCS San Raffaele Scientific Institute, Division of Immunology, Transplantation, and Infectious Diseases, Infection and Cystic Fibrosis Unit, Milan, Italy; 2 IRCCS San Raffaele Scientific Institute, Division of Immunology, Transplantation, and Infectious Diseases, Emerging Bacterial Pathogens Unit, Milan, Italy Objectives: Polymicrobial infections play a key role in driving chronic lung diseases and significantly impact the clinical outcomes. In the case of cystic fibrosis (CF), Staphylococcus aureus infection precedes chronic respiratory colonization by Pseudomonas aeruginosa. Whether and how S. aureus is an independent contributor in the pathogenesis or impacts on the progres- sion of P. aeruginosa chronic infection is not clear. Methods: We established a murine model of chronic lung infection with S. aureus and super-infection with P. aeruginosa reliably mimicking the course of human disease, and evaluated the bacterial load and the host response. Results: In C57Bl/6 mice, S. aureus is more efficient to infect murine lungs when compared to P. aeruginosa. Persisting bacterial cells of S. aureus lead to formation of abscesses while P. aeruginosa lead to airway remodelling and fibrosis. P. aeruginosa promoted an adaptive immune response characterized also by the formation of bronchus-associated lymphoid tissue like structures while S. aureus promoted non-organized B and T cells infiltration. When mice were infected with S. aureus followed by P. aeruginosa, S. aureus favored P. aeruginosa persistence. Notably, the inflammatory response in terms of leukocyte recruitment and cytokine/ chemokines production was similar in mice infected by P. aeruginosa regardless of S. aureus pre-infection and abscesses formation. Poster Sessions / Journalof Cystic Fibrosis 16S1 (2017) S63–S174 S108